2. FREDERICK GRIFFITH
2
British bacteriologist (born October 3,
1877, Eccleston, Lancashire, England—
died 1941, London)
Performed an experiment on Bacterium
Streptococcus pneumoniae (causative
agents of pneumococcal infection)
Griffith's experiments (1928) first
demonstrated that genetic information
could be transferred. Without knowing
what this information was, he called it
the "Transforming Principle".
It was the first step towards Proving that
Nucleic Acids and not the Proteins are
the chemical basis of experiment.
3/14/2024
3. FREDERICK GRIFFITH
He was studying Pathogenicity of different strains of bacteria-
Diplococcus Pneumoniae
*He studied the effect of two different strains of bacteria.
“R” Strain -rough colonies devoid of mucilaginous sheath -
non virulent (non-infectious)
“S” Strain -form smooth colonies having mucilaginous
sheath - virulent (strongly infectious)
4. FREDERICK GRIFFITH
1) R strain Injected in mice- mice survived
2) S strain Injected in mice- mice died
3) Heat killed S strain Injected in mice- mice survived
4) Heat killed S strain + R strain Injected in mice- mice died
5. Griffith’s Conclusion
• Based on the observation, Griffith
concluded that R strain bacteria
had been transformed by the heat-
killed S strain bacteria.
• The R strain inherited some
'transforming principle' from the
heat- killed S strain bacteria and
had enabled the R-strain to
synthesize a smooth
polysaccharide coat which made
them virulent.
• He assumed this transforming
principle as genetic material.
6. DNA and Genetic material
• Griffith's experiment was a turning point towards the
discovery of hereditary material.
• However, it failed to explain the biochemistry of genetic
material.
• Hence, a group of scientists, Oswald Avery, Colin MacLeod
and Maclyn McCarty continued the Griffith experiment in
search of biochemical nature of the hereditary material.
• Their discovery revised the concept of protein as genetic
material to DNA.
7. Avery, MacLeod and McCarty's conclusion
• They repeated Griffith’s Experiment on 1944
• They extracted and purified proteins, DNA, RNA
and other biomolecules from the heat-killed S strain
bacteria.
• They discovered that DNA is the genetic material
and it is alone responsible for the transformation of
the R strain bacteria.
8. Avery, MacLeod and McCarty's conclusion
• They observed that protein-digesting enzymes (proteases) and RNA-
digesting enzymes (RNases) didn't inhibit transformation but DNase did.
• Although it was not accepted by all, they concluded DNA as
genetic material.
